U.S. patent number 8,306,084 [Application Number 12/809,849] was granted by the patent office on 2012-11-06 for laser light source.
This patent grant is currently assigned to Osram Opto Semiconductors GmbH. Invention is credited to Peter Brick, Wolfgang Reill, Uwe Strauss, Soenke Tautz.
United States Patent |
8,306,084 |
Reill , et al. |
November 6, 2012 |
Laser light source
Abstract
A laser light source comprises, in particular, a semiconductor
layer sequence (10) having an active layer having at least two
active regions (45) which are suitable for emitting electromagnetic
radiation during operation via a side area of the semiconductor
layer sequence (10) along an emission direction (90), said side
area being embodied as a radiation coupling-out area (12), a
respective electrical contact area (30) above each of the at least
two active regions (45) on a main surface (14) of the semiconductor
layer sequence (10), and a surface structure in the main surface
(14) of the semiconductor layer sequence (10), wherein the at least
two active regions (45) are arranged in a manner spaced apart from
one another in the active layer (40) transversely with respect to
the emission direction (90), each of the electrical contact areas
(30) has a first partial region (31) and a second partial region
(32) having a width that increases along the emission direction
(90) toward the radiation coupling-out area (12), the surface
structure has, between the at least two electrical contact areas
(30), at least one first depression (6) along the emission
direction (90) and also second depressions (7), and the first
partial regions (31) of the electrical contact areas (30) are in
each case arranged between at least two second depressions (7).
Inventors: |
Reill; Wolfgang (Pentling,
DE), Tautz; Soenke (Tegernheim, DE), Brick;
Peter (Regensburg, DE), Strauss; Uwe (Bad Abbach,
DE) |
Assignee: |
Osram Opto Semiconductors GmbH
(Regensburg, DE)
|
Family
ID: |
40690049 |
Appl.
No.: |
12/809,849 |
Filed: |
December 16, 2008 |
PCT
Filed: |
December 16, 2008 |
PCT No.: |
PCT/DE2008/002123 |
371(c)(1),(2),(4) Date: |
September 15, 2010 |
PCT
Pub. No.: |
WO2009/080011 |
PCT
Pub. Date: |
July 02, 2009 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
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US 20110051766 A1 |
Mar 3, 2011 |
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Foreign Application Priority Data
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Dec 21, 2007 [DE] |
|
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10 2007 061 922 |
Mar 12, 2008 [DE] |
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10 2008 013 896 |
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Current U.S.
Class: |
372/45.01;
372/50.12 |
Current CPC
Class: |
H01S
5/4031 (20130101); H01S 5/22 (20130101); H01S
5/1017 (20130101); H01S 5/1064 (20130101) |
Current International
Class: |
H01S
5/00 (20060101) |
Field of
Search: |
;372/45.01,50.12 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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197 17 571 |
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Oct 1998 |
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DE |
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103 16 220 |
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Nov 2004 |
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DE |
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0 624 284 |
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Jan 1993 |
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EP |
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2 879 840 |
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Jun 2006 |
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FR |
|
Primary Examiner: Park; Kinam
Attorney, Agent or Firm: Cozen O'Connor
Claims
The invention claimed is:
1. A laser light source, comprising: a semiconductor layer sequence
having an active layer having at least two active regions which are
suitable for emitting electromagnetic radiation during operation
via a side area of the semiconductor layer sequence along an
emission direction, said side area being embodied as a radiation
coupling-out area; a respective electrical contact area above each
of the at least two active regions on a main surface of the
semiconductor layer sequence; and a surface structure in the main
surface of the semiconductor layer sequence, wherein the at least
two active regions are arranged in a manner spaced apart from one
another in the active layer transversely with respect to the
emission direction, each of the electrical contact areas has a
first partial region and a second partial region having a width
that increases along the emission direction toward the radiation
coupling-out area, the surface structure has, between the at least
two electrical contact areas, at least one first depression along
the emission direction and also second depressions, the first
partial regions of the electrical contact areas are in each case
arranged between at least two second depressions, the main surface
comprises ridge-type structures with the electrical contact areas,
each of the ridge-type structures has a first depth in the first
partial region of the electrical contact areas and a second depth
in the second partial region of the electrical contact areas, and
the first depth is greater than the second depth.
2. The laser light source as claimed in claim 1, wherein the second
partial regions in each case have a trapezoidal form and in each
case adjoin the radiation coupling-out area.
3. The laser light source according to claim 1, wherein the first
partial regions in each case extend with a constant width on the
main surface along the emission direction.
4. The laser light source as claimed in claim 1, wherein the active
layer is arranged between two waveguide layers on a substrate and
the first depression extends from the main surface into at least
one layer selected from the active layer, the waveguide layers and
the substrate.
5. The laser light source as claimed in claim 1, wherein the first
depression extends on the main surface from the radiation
coupling-out area to a side area of the semiconductor layer
sequence, said side area lying opposite the radiation coupling-out
area.
6. The laser light source as claimed in claim 1, wherein the first
depression has at least one trench parallel to the emission
direction.
7. The laser light source as claimed in claim 1, wherein the first
depression has sidewalls which form an angle of greater than or
equal to 90.degree. with the main surface.
8. The laser light source as claimed in claim 1, wherein an
absorbent material is arranged in the first depression and/or in
the second depression.
9. The laser light source as claimed in claim 1, wherein at least
one second depression has an extension direction which forms an
angle of greater than 0.degree. and less than or equal to
90.degree. with the emission direction.
10. The laser light source as claimed in claim 1, wherein at least
one second depression is at a distance of less than or equal to 4
.mu.m from an electrical contact area.
11. The laser light source as claimed in claim 1, wherein the
active layer is arranged between two waveguide layers on a
substrate and at least one second depression extends from the main
surface right into at least one layer selected from the active
layer, the waveguide layers and the substrate.
12. The laser light source as claimed in claim 1, wherein at least
one second depression has sidewalls which form an angle of greater
than or equal to 90.degree. with the main surface.
13. The laser light source as claimed in claim 1, wherein the main
surface comprises an etching stop layer, which adjoins the
ridge-type structures.
14. The laser light source as claimed in claim 1, wherein the
semiconductor layer sequence comprises, at a distance from the at
least two active regions, at least one further active region in the
active layer, the main surface has a further electrical contact
area having a first and second partial region above the further
active region, the surface structure has at least one further first
depression along the emission direction, which is arranged between
the at least two electrical contact areas and the further
electrical contact area, and the surface structure has two further
second depressions between which the first partial region of the
further electrical contact area is arranged.
15. The laser light source as claimed in claim 1, wherein the first
depth of the ridge-type structures extends to a waveguide layer of
the semiconductor layer sequence and creates an index guidance, and
the second depth of the ridge-type structures extends to a
semiconductor contact layer or a cladding layer above the waveguide
layer in the semiconductor layer sequence and creates a gain
guidance.
Description
RELATED APPLICATIONS
This is a U.S. national stage of application No. PCT/DE2008/002123,
filed on Dec. 16, 2008.
This patent application claims the priorities of German Patent
Application 10 2007 061 922.9 filed Dec. 21, 2007 and of German
Patent Application 10 2008 013 896.7 filed Mar. 12, 2008, the
disclosure contents of both of which are hereby incorporated by
reference.
FIELD OF THE INVENTION
The present invention is related to a laser light source comprising
a semiconductor layer sequence.
BACKGROUND OF THE INVENTION
Laser systems for optical applications, for instance projection
applications, and also for laser pump sources for coupling into
optical fibers require a high brilliance, that is to say a high
power and a high beam quality. The latter is given by the so-called
beam parameter product, that is to say the product of the beam
waist radius and the divergence angle of the light emitted by the
laser. Furthermore, for material processing applications and for
pump lasers for solid-state lasers, for instance, it may be
desirable to use lasers having a high power in conjunction with a
small emission area.
SUMMARY OF THE INVENTION
One object of at least one embodiment is to provide a laser light
source comprising a semiconductor layer sequence having at least
two active regions.
In accordance with at least one embodiment, a laser light source
comprises, in particular, a semiconductor layer sequence having an
active layer having at least two active regions which are suitable
for emitting electromagnetic radiation during operation via a side
area of the semiconductor layer sequence along an emission
direction, said side area being embodied as a radiation
coupling-out area, a respective electrical contact area above each
of the at least two active regions on a main surface of the
semiconductor layer sequence, and a surface structure in the main
surface of the semiconductor layer sequence, wherein the at least
two active regions are arranged in a manner spaced apart from one
another in the active layer transversely with respect to the
emission direction, each of the electrical contact areas has a
first partial region and a second partial region having a width
that increases along the emission direction toward the radiation
coupling-out area, the surface structure has, between the at least
two electrical contact areas, at least one first depression along
the emission direction and also second depressions, and the first
partial regions of the electrical contact areas are in each case
arranged between at least two second depressions.
Here and hereinafter "transversely" can mean that a first direction
embodied transversely with respect to a second direction has at
least one direction component which is perpendicular to the second
direction. In particular, that can mean that the first direction is
perpendicular to the second direction.
Here and hereinafter "light" or "electromagnetic radiation" can
equally mean, in particular, electromagnetic radiation having at
least one wavelength or a wavelength range from an infrared to
ultraviolet wavelength range. In particular, the light or the
electromagnetic radiation can encompass a visible, that is to say a
red to blue, wavelength range having one or more wavelengths of
between approximately 450 nm and approximately 700 nm. In this
case, the semiconductor layer sequence can generate coherent
electromagnetic radiation brought about by stimulated emission, in
particular, during operation, which radiation can be characterized
for instance by a spectrum in a wavelength range having a spectral
width of less than 10 nm and preferably less than 5 nm.
Furthermore, the coherent electromagnetic radiation can have a
coherence length of an order of magnitude of meters up to an order
of magnitude of hundred meters or more. In this case, each active
region can emit its own radiation beam of coherent electromagnetic
radiation. The radiation beams can in each case have beam
properties similar or identical to an ideal. Gaussian radiation
beam.
The semiconductor layer sequence having at least two active regions
can be suitable for increasing the power or the intensity of the
electromagnetic radiation emitted by the laser light source in
comparison with a laser light source having only one active region.
In particular, the laser light source can be embodied as a
so-called laser bar having a plurality of active regions.
The radiation beams of coherent electromagnetic radiation
respectively emitted by the active regions can furthermore be
collimatable and/or focusable in a radiation beam. For this
purpose, it is possible to dispose downstream of the radiation
coupling-out area of the semiconductor layer sequence, and in
particular downstream of the active regions, a collimation or
focusing optical unit such as, for instance, one or more anamorphic
lenses, for instance one or more cylindrical lenses, by means of
which the electromagnetic radiation can be collimated and/or
focused to form a radiation beam.
In order to generate coherent electromagnetic radiation by means of
stimulated emission, the radiation coupling-out area and/or that
side area of the semiconductor layer sequence which lies opposite
the radiation coupling-out area, and which can also be referred to
as the rear side, can be embodied as at least partly reflective. As
a result, the radiation coupling-out area and the rear side can
form an optical resonator for the electromagnetic radiation
generated in the active regions. In this case, it can be possible
that one or more standing electromagnetic waves corresponding to
one or more of the modes predefined by the optical resonator in the
active regions form in each of the at least two active regions. In
particular, the modes that form in the at least two active regions
can differ for instance in terms of their relative phase angle with
respect to one another.
The radiation coupling-out area and the rear side of the
semiconductor layer sequence can be producible for example by
cleavage of the semiconductor layer sequence along a crystal plane.
Furthermore, the radiation coupling-out area and/or the rear side
of the semiconductor layer sequence can have a reflective coating,
for instance in the form of Bragg mirrors.
Since the active regions are arranged in the same active layer, it
can be possible in known laser bars having a plurality of active
regions that so-called optical crosstalk can take place between the
active regions. Said optical crosstalk can be brought about, in
principle, by the coherent electromagnetic radiation which is
generated by one active region and which can be backscattered into
the same active region or scattered or directed into another active
region. Furthermore, it can also be possible that besides the
stimulated emission which can preferably lead to the generation of
the coherent electromagnetic radiation in the active regions,
incoherent electromagnetic radiation can be generated and emitted
isotropically as a result of spontaneous emission that additionally
takes place. Therefore, incoherent electromagnetic radiation
generated in this way can be radiated from one active region into
another active region. Such electromagnetic radiation which
propagates within the semiconductor layer sequence and can be
radiated into an active region is referred to hereinafter as stray
radiation. The stray radiation can disturb the formation of
standing waves, that is to say of electromagnetic field modes, in
the active regions, which can result in a reduction of the power or
intensity respectively emitted by the active regions and also a
reduction of the beam quality.
By virtue of the fact that the laser light source described here
comprises a surface structure having at least one first depression
and second depressions, the stray radiation is prevented from
propagating in the semiconductor layer sequence. Furthermore, the
optical crosstalk can thereby be reduced or prevented. The beam
quality of the electromagnetic radiation emitted by the active
regions of the laser light source, for example measurable in the
form of the beam quality factor M.sup.2 known to the person skilled
in the art, can thus be significantly improved in comparison with
conventional laser bars.
The semiconductor layer sequence can be embodied as an epitaxial
layer sequence or as a radiation-emitting semiconductor chip
comprising an epitaxial layer sequence, that is to say as a
semiconductor layer sequence grown epitaxially. In this case, the
semiconductor layer sequence can be embodied on the basis of
AlGaAs, for example. AlGaAs-based semiconductor chips and
semiconductor layer sequences include, in particular, those in
which the semiconductor layer sequence produced epitaxially
generally has a layer sequence composed of different individual
layers containing at least one individual layer which comprises a
material from the III-V compound semiconductor material system
Al.sub.xGa.sub.1-xAs where 0.ltoreq.x.ltoreq.1. In particular, an
active layer comprising an AlGaAs-based material can be suitable
for emitting electromagnetic radiation having one or more spectral
components in a red to infrared wavelength range. Furthermore, a
material of this type can comprise In and/or P in addition or as an
alternative to the elements mentioned.
Furthermore, the semiconductor layer sequence can be embodied on
the basis of InGaAlN, for example. InGaAlN-based semiconductor
chips and semiconductor layer sequences include, in particular,
those in which the semiconductor layer sequence produced
epitaxially generally has a layer sequence composed of different
individual layers containing at least one individual layer which
comprises a material from the III-V compound semiconductor material
system In.sub.xAl.sub.yGa.sub.1-x-yN where 0.ltoreq.x.ltoreq.1,
0.ltoreq.y.ltoreq.1 and x+y.ltoreq.1. Semiconductor layer sequences
having at least one active layer on the basis of InGaAlN can, for
example, preferably emit electromagnetic radiation in an
ultraviolet to green wavelength range.
As an alternative or in addition, the semiconductor layer sequence
or the semiconductor chip can also be based on InGaAlP, that is to
say that the semiconductor layer sequence can have different
individual layers, at least one individual layer of which comprises
a material from the III-V compound semiconductor material system
In.sub.xAl.sub.yGa.sub.1-x-yP where 0.ltoreq.x.ltoreq.1,
0.ltoreq.y.ltoreq.1 and x+y.ltoreq.1. Semiconductor layer sequences
or semiconductor chips which have at least one active layer on the
basis of InGaAlP can, for example, preferably emit electromagnetic
radiation having one or more spectral components in a green to red
wavelength range.
As an alternative or in addition, the semiconductor layer sequence
or the semiconductor chip can also comprise II-VI compound
semiconductor material systems besides or instead of the III-V
compound semiconductor material systems.
The semiconductor layer sequence can furthermore have a substrate
on which the abovementioned III-V or II-VI compound semiconductor
material systems are deposited. In this case, the substrate can
comprise a semiconductor material, for example a compound
semiconductor material system mentioned above. In particular, the
substrate can comprise GaP, GaN, SiC, Si and/or Ge or be composed
of such a material.
The semiconductor layer sequence can have, as active regions in the
active layer, for example, conventional pn junctions, double
heterostructures, single quantum well structures (SQW structures)
or multiple quantum well structures (MQW structures). The
semiconductor layer sequence can comprise, besides the active layer
having the active regions, further functional layers and functional
regions, for instance p- or n-doped charge carrier transport
layers, that is to say electron or hole transport layers, p- or
n-doped confinement, cladding or waveguide layers, barrier layers,
planarization layers, buffer layers, protective layers and/or
electrodes and combinations thereof. In this case, the electrodes
can each have one or more metal layers comprising Ag, Au, Sn, Ti,
Pt, Pd and/or Ni. Such structures concerning the active layer or
the further functional layers and regions are known to the person
skilled in the art in particular with regard to construction,
function and structure and, therefore, will not be explained in any
greater detail at this juncture.
Furthermore, additional layers, for instance buffer layers, barrier
layers and/or protective layers, can also be arranged around the
semiconductor layer sequence, for example, perpendicularly to the
growth direction of the semiconductor layer sequence, that is to
say, for instance, on the side areas of the semiconductor layer
sequence.
Furthermore, the semiconductor layer sequence can be embodied as a
so-called "distributed feedback laser", DFB laser for short. DFB
lasers of this type have active regions which are periodically
structured in the emission direction. A periodically structured
active region has periodically arranged regions having alternating
refractive indices which can form an interference grating or
interference filter which can lead to wavelength-selective
reflection.
By virtue of a side area of the semiconductor layer sequence being
embodied as a radiation coupling-out area, the semiconductor layer
sequence can preferably be an edge emitting laser diode.
Preferably, the semiconductor layer sequence can in this case have
a first and a second waveguide layer between which the active layer
with the active regions is arranged and which enable guidance of
the electromagnetic radiation generated in the active regions in
the active layer.
The main surface with the electrical contact areas and the surface
structure can have a main extension plane, which can be
perpendicular to the growth direction of the semiconductor layer
sequence. In particular, the main surface with the electrical
contact areas and the surface structure can be a surface of the
semiconductor layer sequence which lies opposite a substrate.
The electrical contact areas on the main surface can be embodied,
in particular, as such area regions of the main surface which are
electrically conductively connected to an electrode applied on the
main surface. For this purpose, by way of example, an electrode
layer, which can comprise one of the abovementioned metals, for
instance, can be applied in a structured fashion in the form of the
electrical contact areas on the main surface.
As an alternative or in addition, an electrically insulating layer
can be applied on the main surface in a structured fashion in such
a way that the electrical contact areas are free of the
electrically insulating layer and an electrode layer is applied in
a structured fashion or in a large-area fashion above the
electrically insulating layer and the electrical contact areas on
the main surface. As an alternative or in addition, the
semiconductor layer sequence can have, in a structured fashion in
the regions of the electrical contact areas, a layer comprising a
highly doped semiconductor material which enables an ohmic
electrical contact with an electrode, this ohmic electrical contact
having a low contact resistance in comparison with the rest of the
main surface.
By virtue of the form of the electrical contact areas and the
electrical conductivities of the functional layers in the growth
direction and also in the extension plane of the semiconductor
layer sequence, the active regions can form below the active
contact areas in the active layer, in which active regions the
current density is high enough to enable stimulated emission of
coherent electromagnetic radiation. In a manner corresponding to
the first and second partial regions of the electrical contact
areas, the active regions can have precisely such first and second
partial regions. The mode structure of the standing electromagnetic
waves generated in the active regions can thus be influenced by the
form of the electrical contact areas. The emission direction of the
semiconductor layer sequence can correspond to the main extension
direction of the electrical contact areas and thus the main
extension direction of the active regions.
In this case, it can be advantageous if the first partial region of
an electrical contact area extends along the emission direction
with a constant width on the main surface. In particular, the first
partial regions of the at least two electrical contact areas can in
this case be embodied as strips arranged parallel to one another.
The first partial regions of the electrical contact areas can
furthermore adjoin the rear side of the semiconductor layer
sequence lying opposite the radiation coupling-out area. In this
case, the width of the first partial regions can be less than or
equal to 20 .mu.m, preferably less than or equal to 10 .mu.m, and
particularly preferably less than or equal to 5 .mu.m.
The first partial region of an electrical contact area can
furthermore directly adjoin the second partial region. That can
mean that the second partial region, in a boundary region in which
the second partial region adjoins the first partial region, has the
same width as the first partial region. In particular, the second
partial region can in this case widen linearly away from the first
partial region in the emission direction. That can mean, in
particular, that the second partial region has a trapezoidal form,
which can furthermore be symmetrical with respect to the emission
direction. In this case, the second partial region can widen in the
emission direction to a width of greater than or equal to 50 .mu.m,
greater than or equal to 100 .mu.m, or greater than or equal to 200
.mu.m. In particular, the aperture angle at which the second
partial region widens can be greater than or equal to 1.degree. and
less than or equal to 10.degree., and in particular greater than or
equal to 2.degree. and less than or equal to 6.degree., which
results from the Gaussian formalism of diffraction-limited beams.
The guidance of the electromagnetic radiation in the second partial
region can in this case be effected according to the principle of
gain guidance, which means that an at least virtually Gaussian beam
is generated in the first partial region, for which beam large
diffraction angles can be possible on account of the small width of
the first partial region. Furthermore, the virtually Gaussian beam
can diffract from the first partial region freely into the second
partial region and effectively gain in power during propagation
along the second partial region. In this case, the second partial
region can adjoin the radiation coupling-out area via which
electromagnetic radiation that is generated in the active region
and amplified can be emitted directly.
In this case, it can be advantageous if layers of the semiconductor
layer sequence are structured in ridge-type fashion in such a way
that the main surface with the electrical contact areas comprises
the ridge-type structures. In particular, such a configuration of
the main surface of the semiconductor layer sequence, which
configuration is also known as a "ridge structure" or ridge
waveguide structure, can be suitable for making possible, depending
on its width and height and as a result of the so-called index
guidance brought about on account of the ridge-type structure and
associated jump in refractive index of from approximately 0.005 to
0.01, the formation of a transverse fundamental mode in the active
region. In this case, the height of a ridge structure can influence
said jump in refractive index to a greater extent than the width.
The width and height of the ridge structure can furthermore also
determine the aperture angle of the virtually Gaussian beam from
the first partial region upon entering into the second partial
region of an active region. In particular, the main surface has
such ridge-type structures or ridge structures on which the first
and the second partial regions of the electrical contact areas are
in each case arranged.
In this case, by way of example, the ridge structure can be
structured as far as a first depth in the first partial region and
as far as a second depth in the second partial region, wherein the
first and second depths can be identical or different. In
particular by way of example, the first depth for index guidance
can extend as far as a waveguide layer, while the second depth for
gain guidance described above can extend as far as a semiconductor
contact layer or cladding layer arranged above the waveguide layer.
Furthermore, the first depth can also extend right into the
cladding layer, while the second depth can extend as far as an
interface between the cladding layer and a semiconductor contact
layer arranged thereabove or even only into the semiconductor
contact layer.
In order to produce the ridge structure it is possible, by way of
example, to provide a semiconductor layer sequence having the
functional layers mentioned above. The ridge structure can then be
produced through a mask by means of a removing method, for instance
etching, on the main surface of the semiconductor layer sequence.
In this case, the width of the ridge structure in the first and
second partial regions of the subsequent electrical contact area
can be settable by means of a mask which can be produced
photolithographically. In order to obtain a defined and uniform
height of the ridge structure, the semiconductor layer sequence can
have a so-called etching stop layer. In the case of a semiconductor
layer sequence comprising AlGaAs-based materials, for example, the
etching stop layer can have an Al-free, P-containing layer in a
layer or between two layers of the semiconductor layer sequence. In
this case, by way of example, the etching stop layer can comprise
an Al-free, P-containing GaAs semiconductor material and/or InGaP
or be composed thereof. By way of example, the etching stop layer
can be arranged in a waveguide layer arranged between the active
layer and the main surface. In this case, the thickness, doping
and/or position of the etching stop layer in the waveguide layer
can be adapted to the waveguide layer. In this case, after etching,
the etching stop layer can adjoin the ridge structure and form a
part of the main surface.
In order to avoid the above-described optical crosstalk between the
active regions, the first depression can project from the main
surface into the semiconductor layer sequence to an extent such
that propagation of the stray radiation in the semiconductor layer
sequence can be reduced or prevented. In this case, the first
depression can extend into one of the functional layers of the
semiconductor layer sequence. The fact that the first depression
"extends into a layer" can mean that the first depression ends in
the layer and the layer has a smaller thickness in the region of
the first depression than alongside the first depression. It can
furthermore mean that the first depression penetrates right through
the layer and therefore extends as far as an interface with a
further layer arranged below the layer. By way of example, the
semiconductor layer sequence can have two waveguide layers, between
which the active layer is arranged. The first depression can extend
at least into the waveguide layer between the active layer and the
main surface. Furthermore, the first depression can extend right
into the active layer or right into the waveguide layer arranged
below the active layer, as viewed from the main surface.
Furthermore, the first depression can extend right into a layer
below the waveguide layers and the active layer, for instance a
cladding or intermediate layer, or as far as a substrate on which
the functional layers are applied.
Furthermore, the first depression can extend on the main surface
from the radiation coupling-out area as far as the rear side of the
semiconductor layer sequence lying opposite the radiation
coupling-out area. In this case, by way of example, the first
depression can comprise at least one trench which extends parallel
to the active regions along the emission direction. As an
alternative or in addition, the first depression can also have a
plurality of trenches or depressions arranged alongside one another
and/or one behind another.
The first depression can have sidewalls which can extend along the
growth direction of the semiconductor layer sequence and form an
angle of greater than or equal to 90.degree. with the main surface.
In this case, an angle of 90.degree. can mean that the first
depression has sidewalls which are embodied parallel to the growth
direction of the semiconductor layer sequence and thus
perpendicularly to the main surface. An angle of greater than
90.degree. means that the edge between a sidewall of the first
depression and the main surface forms an obtuse angle.
Consequently, the cross section of the first depression decreases
in a direction as viewed from the main surface into the
semiconductor layer sequence. In this case, the first depression
can have a V-shaped or U-shaped cross section or a combination
thereof. In particular, the first depression can have sidewalls
which form an edge having an angle of less than or equal to
135.degree., and preferably equal to 135.degree., with the main
surface. As a result, stray radiation which propagates in the
semiconductor layer sequence and impinges on the sidewall of the
first depression can be reflected downward, as viewed from the main
surface, into functional layers lying below the active layer and/or
a substrate and be absorbed therein. For this purpose, the
semiconductor layer sequence can for example additionally have a
layer comprising an absorbent material below the active layer.
Furthermore, the first depression can be at least partly filled
with an absorbent material. That can mean that at least the
sidewalls of the first depression can be coated with an absorbent
material. Stray radiation which propagates in the semiconductor
layer sequence and impinges on the first depression can therefore
be absorbed and prevented from further propagation in the
semiconductor layer sequence.
The absorbent material can comprise, for example, gallium,
aluminum, chromium or titanium or a combination thereof.
Furthermore, the absorbent material can comprise a semiconductor
material, for instance silicon, germanium, InAlGaAs, InGaAlP and
InGaAlN, ZnSe and/or ZnS. The semiconductor material can preferably
have a band gap which is less than or equal to the wavelength of
the electromagnetic radiation generated in the active regions.
Furthermore, the absorbent material can comprise antimony or a
layer or a layer stack comprising antimony with one or more of the
materials N, Te, Ge, Ag and In, for example antimony nitride
(SbN.sub.x), SbTe, GeSbTe and/or AgInSbTe. As an alternative or in
addition, the first filter element can also have a layer or a layer
stack comprising AgO.sub.x, PtO.sub.x and/or PdO.sub.x. Such layers
or layer stacks are also known as "super-resolution near-field
structure" (super-RENS), which, below a limit temperature, can be
non-transparent and absorbent to electromagnetic radiation.
By virtue of the first depression described here, the at least two
active regions can thus be effectively optically isolated, such
that optical crosstalk between the active regions can no longer
take place.
Furthermore, at least one second depression of the second
depressions, as described in connection with the first depression,
can extend into a layer of the semiconductor layer sequence, for
instance into a waveguide layer, into the active layer or into the
substrate. Furthermore, at least one second depression can have
sidewalls which can form an angle of greater than or equal to
90.degree. and less than or equal to 135.degree. with the main
surface and can therefore form a right-angled or obtuse-angled edge
with the main surface. In particular, the second depressions can be
embodied in an identical fashion with regard to their depth, size
and cross-sectional form.
At least one second depression can have an extension direction
which can form an angle of greater than 0.degree. and less than
90.degree. with the emission direction. Preferably, the angle can
be greater than or equal to 30.degree. and less than or equal to
60.degree., and particularly preferably approximately 45.degree..
That can mean that the at least one second depression comprises a
trench or is embodied as a trench and is arranged obliquely with
respect to the emission direction.
In particular, that can also mean that the at least one second
depression is also arranged obliquely with respect to the radiation
coupling-out area. As a result, it can be possible that
electromagnetic radiation which is reflected at the radiation
coupling-out area and can propagate as stray radiation in the
semiconductor layer sequence counter to the emission direction in a
manner laterally offset with respect to the active region can be
reflected by the second depression in the direction of the first
depression and, as described above, can likewise be reflected or
else absorbed by the latter. Laser oscillations possibly occurring
alongside the active region can thereby be prevented, such that no
secondary modes which could impair the beam quality of the
electromagnetic radiation generated by the active region occur in
the active layer.
Furthermore, at least one second depression, as described above in
connection with the first depression, can be at least partly filled
or coated with an absorbent material.
In particular, the second depressions can be embodied in an
identical fashion, wherein in each case two second depressions can
be arranged around a first partial region of an electrical contact
area symmetrically with respect to the emission direction. In this
case the second depressions can be at a distance of less than or
equal to 4 .mu.m from an active region and/or a ridge structure or
electrical contact area. Precisely by virtue of the fact that the
second depressions are arranged alongside the first partial regions
of the electrical contact areas in such a way that the first
partial regions are situated between in each case two second
depressions, diaphragms in the semiconductor layer sequence can be
made possible by means of the second depressions, said diaphragms
having a smallest possible diaphragm aperture. In particular, it
can be advantageous in this case if the second depressions are
arranged closer to the second partial region than to the rear side
of the semiconductor layer sequence.
In order to avoid, in particular, the arising of stray radiation as
a result of reflection of coherent electromagnetic radiation
generated in the active region at the radiation coupling-out area,
the radiation coupling-out area can have a layer having a
reflectivity of less than or equal to 10%, preferably less than or
equal to 5%, and particularly preferably less than or equal to 2%,
such that the radiation coupling-out area can have a transmission
coefficient of greater than or equal to 90%, preferably greater
than or equal to 95%, and particularly preferably greater than or
equal to 98%. In particular, a reflection coefficient of 0.1 to 2%
can be advantageous. By way of example, the layer can be embodied
as an individual layer or as a layer sequence having layer pairs
and in this case can comprise metal or semimetal oxides and/or
metal or semimetal nitrides. A metal oxide or a semimetal oxide can
comprise aluminum, silicon, titanium, zirconium, tantalum, niobium,
or hafnium. Furthermore, a nitride can comprise at least one of
said metals and semimetals, for example silicon nitride.
Particularly preferably, the metal oxide or the semimetal oxide
comprises at least one of the materials niobium pentoxide, hafnium
dioxide, aluminum oxide, silicon dioxide, titanium dioxide,
tantalum pentoxide and zirconium dioxide.
Furthermore, the semiconductor layer sequence can have a
multiplicity of active regions with associated electrical contact
areas on the main surface. That can mean, in particular, that the
semiconductor layer sequence has at least one further active region
and a further electrical contact area having a first and second
partial region which are arranged transversely with respect to the
emission direction alongside the at least two active regions and
the associated electrical contact areas, respectively. Furthermore,
the semiconductor layer sequence can have on the main surface at
least one further first depression between the at least two
electrical contact regions and the further electrical contact
region. Furthermore, on the main surface, a further two second
depressions can be arranged, between which the first partial region
of the further electrical contact area is arranged.
The laser light source described here enables a high emission power
with at the same time high beam quality. In comparison therewith,
known broad stripe laser diodes, which can have an active region
having a width of the order of magnitude of hundreds of .mu.m, have
admittedly a high emission power but associated therewith also an
emission characteristic having a plurality of electromagnetic modes
and also a greatly asymmetrical beam profile as a consequence of
the asymmetrical beam parameter product with respect to the beam
axes parallel to the extension plane of the semiconductor layers
("slow axis") and parallel to the growth direction of the
semiconductor layer sequence ("fast axis"). As a result, a broad
stripe laser usually requires, in contrast to the laser light
source described here, a complex and expensive optical unit in
order to symmetrize the emission characteristic. In contrast to
known trapezoidal laser bar embodiments, the laser light source
described here also enables a high beam quality with at the same
time high power. In this case, the laser light source described
here can be producible in a cost-effective manner.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B show schematic illustrations of a laser light
source in accordance with one exemplary embodiment,
FIGS. 2A to 2C show schematic illustrations of a laser light source
in accordance with a further exemplary embodiment, and
FIGS. 3A to 5B show measurements of laser light sources in
accordance with further exemplary embodiments.
DETAILED DESCRIPTION OF THE DRAWINGS
In the exemplary embodiments and figures, identical or identically
acting constituent parts can be provided in each case with the same
reference symbols. The illustrated elements and their size
relationships among one another should not be regarded as true to
scale, in principle; rather, individual elements such as, for
example, layers, structural parts, components and regions may be
illustrated with exaggerated thickness or size dimensions in order
to enable better illustration and/or in order to afford a better
understanding.
FIGS. 1A and 1B show an exemplary embodiment of a laser light
source. Unless expressly indicated otherwise, the following
description concerning this exemplary embodiment refers equally to
both FIGS. 1A and 1B.
In this case, FIG. 1A shows a schematic three-dimensional
illustration of the laser light source comprising a semiconductor
layer sequence 10. FIG. 1B shows a plan view of the laser light
source from the direction identified by BB in FIG. 1A.
The laser light source in accordance with the exemplary embodiment
in FIGS. 1A and 1B has a semiconductor layer sequence 10 comprising
a substrate 1, on which a plurality of functional, epitaxially
grown layers 4 are applied. In this case, in the exemplary
embodiment shown, the semiconductor layer sequence 10 is formed by
a GaAs substrate 1 and thereabove a 100 nm thick intermediate or
cladding layer 41 composed of AlGaAs having an Al proportion of
approximately 40% of the group III materials and/or composed of
InGaP having an In proportion of approximately 50% of the group III
materials, and thereabove a 2 .mu.m thick InAlP waveguide layer 42,
thereabove a 100 nm thick InGaAlP/InGaP quantum film/barrier layer
MWQ structure having an In proportion of approximately 50% and an
Al proportion of approximately 25%, thereabove a 2 .mu.m thick
InAlP waveguide layer 43 and thereabove a 100 nm thick InGaP
intermediate or cladding layer 44. In addition, a contact layer,
for instance a 300 nm thick GaAs contact layer 47, is arranged on
the cladding layer 44. A semiconductor layer sequence 10 of this
type can be suitable for generating yellow to infrared
electromagnetic radiation, and particularly preferably
electromagnetic radiation in a red wavelength range.
As an alternative to the arsenide-based semiconductor materials
described here, the semiconductor layer sequence 10 can also
comprise nitride-based semiconductor materials, for example. A
semiconductor layer sequence 10 of this type can be suitable for
generating electromagnetic radiation in an ultraviolet to green and
preferably in a blue wavelength range.
In this case, the substrate 1 can be a growth substrate on which
the functional layers are grown epitaxially. As an alternative
thereto, the semiconductor layer sequence can be producible using
thin-film technology. That means that the functional layers are
grown on a growth substrate and subsequently transferred to a
carrier substrate, which then forms the substrate 1 of the
semiconductor layer sequence 10. In this case, depending on the
growth technique, the n-conducting layers or the p-conducting
layers of the semiconductor layer sequence 10 can face the
substrate 1.
Furthermore, the semiconductor layer sequence 10 has a radiation
coupling-out area 12 and a surface 13 lying opposite the latter and
embodied as a rear side, which in each case have an at least partly
reflective coating (not shown). As a result, the radiation
coupling-out area 12 and the rear side 13 form an optical
resonator. The respective reflective coating can comprise, for
example, a Bragg mirror layer sequence and/or reflective metal
layers.
Furthermore, passivation layers for protecting the semiconductor
layer sequence can be applied (not shown) on or above the surfaces
of the semiconductor layer sequence which are different than the
radiation coupling-out area.
The electrical contact-connection of the semiconductor layer
sequence 10 is effected by means of an electrode 2 on that surface
of the substrate 1 which is remote from the functional layers 4,
and by means of electrode strips 3 on the main surface 14 of the
functional layers 4 which lies opposite the substrate 1. In this
case, the electrodes 2 and 3 can each have one or more metal layers
comprising Ag, Au, Sn, Ti, Pt, Pd and/or Ni.
As an alternative to the electrical contact-connection by means of
the electrode 2 through the substrate 1, the electrical contact 2
can also be arranged on the same side of the substrate 1 as the
functional layers 4. This type of contact-connection is primarily
suitable for making electrical contact with the functional layers 4
from the substrate side if said layers are arranged on an
electrically non-conductive substrate 1.
The contact areas between the electrode strips 3 and the cladding
layer 44 are embodied as electrical contact areas 30.
As indicated in FIG. 1B, the electrical contact areas 30 each have
a first partial region 31 and a second partial region 32 adjoining
the latter. The imaginary boundary line between the first and
second partial regions is indicated in each case by the line 33.
The second partial regions 32 have a width that increases along the
emission direction 90 towards the radiation coupling-out area 12.
In this case, the partial regions 32 are embodied in trapezoidal
fashion and enable the power of the electromagnetic radiation
generated in the active regions 45 to be amplified.
In the exemplary embodiment shown, the cladding layer 44 is
embodied in ridge-type fashion in the region of the electrical
contact areas 30 in the first partial region 31 and forms with the
contact layer 47 a so-called ridge structure 11 as described in the
general part, wherein the top sides of the ridge structures 11 as
part of the main surface 14 form the electrical contact areas 30.
In the second partial region 32, only the contact layer 47 is
embodied in ridge-type fashion, such that the ridge structures have
a larger depth in the first partial region 31 than in the second
partial region. With regard to their form, the ridge structures 11
have the same form as the electrical contact areas 30.
By virtue of the ridge structures 11, the formation of coherent
electromagnetic radiation in a transverse fundamental mode can be
made possible in the active layer 40, whereas undesired further
laser modes can be suppressed. As a result, the active layer 40 has
active regions 45 below the electrical contact areas 30 and the
ridge structures 11, which active regions are predefined, inter
alia, by the dimensions of the electrical contact areas 30 and of
the ridge structures 11 and are indicated by the hatched areas in
the active layer 40 in the exemplary embodiment shown. In this
case, the active regions 45 extend over the entire length of the
active layer 40 in the resonator formed by the radiation
coupling-out area 12 and the rear side 13. In the active regions
45, the semiconductor layer sequence 10 can generate coherent
electromagnetic radiation by stimulated emission during operation,
which radiation can be emitted as a radiation beam in each case via
the radiation coupling-out area 12 along the emission direction
better defined by 90.
Between the electrical contact areas 30, the main surface 14 has,
as part of a surface structure, a first depression 6 extending over
the main surface 14 along the emission direction 90. In this case,
the first depression 6 is embodied as a trench that extends from
the mains surface 14 right into the substrate 1. In this case, the
first depression 6 in the exemplary embodiment shown has sidewalls
which are perpendicular to the main surface 14 and respectively
form right-angled edges with the main surface 14. In this case, the
first depression 6 extends from the radiation coupling-out area 12
as far as the rear side 13 of the semiconductor layer sequence
10.
By virtue of the first depression 6, the direct propagation of
stray radiation from one active region 45 to the other active
region 45 in the semiconductor layer sequence is no longer
possible, such that the two active regions 45 are optically
decoupled. Furthermore, the first depression can have, at least at
the sidewalls, a layer comprising an absorbent material (not
shown), which layer can comprise germanium, for instance. In order
to avoid an electrical short circuit of the functional layers 4, a
dielectrical layer, for instance silicon oxide, can be arranged
between the sidewalls of the first depression 6 and the layer
comprising the absorbent material.
Furthermore, the surface structure on the main surface 14 comprises
second depressions 7, wherein each of the first partial regions 31
of the electrical contact areas 30 is arranged between two second
depressions 7. In this case, the second depressions 7 each have an
extension direction 92 which forms an angle 91 of approximately
45.degree. with the emission direction 90, as is indicated by way
of example by way of a second depression 7. In each case two of the
second depressions 7 here are arranged symmetrically about the
emission direction 90 and a respective first partial region 31.
Like the first depression 6, the second depressions 7 extend from
the main surface 14 into the substrate 1.
Stray radiation which can propagate for example as a result of the
reflection of electromagnetic radiation generated in the active
regions 45 at the radiation coupling-out area 12 counter to the
emission direction 90 in a manner laterally offset with respect to
the active regions 45 in the semiconductor layer sequence 10 can be
reflected at the second depressions 7 to the first depression 6 or
to side areas of the semiconductor layer sequence 10. The formation
of electromagnetic secondary modes between the radiation
coupling-out area 12 and the rear side 13 can thereby be prevented.
In addition, the second depressions 7, like the first depression 6,
can be at least partly filled with an absorbent material.
In order to reduce stray radiation reflected at the radiation
coupling-out area 12, it is possible to apply on the radiation
coupling-out area 12 a reflection-reducing layer or layer sequence
(not shown) having a reflection coefficient of less than 2%,
particularly preferably less than 1%.
FIGS. 2A to 2C show a further exemplary embodiment of a laser light
source, which constitutes a modification of the exemplary
embodiment shown previously. Unless expressly indicated otherwise,
the following description refers equally to all of FIGS. 2A to 2C.
In this case, the differences and further developments in
comparison with the previous exemplary embodiment are described, in
particular.
In this case, FIG. 2A, like the previous FIG. 1B, shows a plan view
of the laser light source. FIGS. 23 and 2C show sectional views
through the laser light source along the sectional planes
identified by BB and CC in FIG. 2A.
The laser light source in accordance with the exemplary embodiment
in FIGS. 2A to 2C has a plurality of active regions and also a
plurality of electrical contact areas 30. FIG. 2A shows the further
electrical contact area 30' with respect to the two electrical
contact areas 30 by way of example in this regard. The further
electrical contact area 30' has a first partial region 31' and a
second partial region 32', which are shaped like the first and
second partial regions 31, 32 of the electrical contact areas
30.
A further first depression 6 is arranged between the electrical
contact areas 30 and the further electrical contact area 30', said
further first depression corresponding in terms of its
configuration to the first depression 6 between the two electrical
contact areas 34. The first partial region 31' of the further
electrical contact area 30' is furthermore arranged between two
further second depression 7', which are embodied like the second
depressions 7.
As can be discerned from the sectional view BB in FIG. 2B, the
first depressions 6, 6' have a V-shaped cross section. That means
that the first depressions 6, 6' have sidewalls which form an angle
91 of greater than 90.degree. with the main surface 14 and thus
form an obtuse-angled edge with the main surface 14. As a result,
it is possible that stray radiation through the first depressions
6, 6' which propagates in the semiconductor layer sequence 10 along
the active layer 40, for example, can be reflected in the direction
of the substrate 1. The substrate 1, the electrode 2 or an
additional layer of the semiconductor layer sequence 10 (not shown)
can be absorbent, for example, such that further propagation of the
stray radiation can be prevented.
As can be discerned from the section view CC in FIG. 2C, the second
depressions 7, 7' also have a V-shaped cross section. In this case,
in the exemplary embodiment shown, the sidewalls of the second
depressions 7, 7' form an angle of approximately 135.degree. with
the main surface 14, which corresponds to an inclination of
approximately 45.degree. with respect to the growth direction of
the semiconductor layer sequence 10.
The semiconductor layer sequence 10 has besides that in connection
with the previous exemplary embodiment in the waveguide layer 43,
which is arranged between the active layer 40 and the main surface
14, an etching stop layer 46 composed of InGaP. By means of the
etching stop layer 46, as described in the general part, a
precisely defined height of the ridge structures 11 can be
produced, as a result of which the beam quality of the
electromagnetic radiation emitted by the active regions can be
improved.
Arranged above the cladding layer 44 is a GaAs contact layer 47,
which makes possible at the electrical contact areas 30 an ohmic
contact with an electrode 3 applied in a large-area fashion, this
ohmic contact having a low contact resistance. In order to enable
current injection only via the electrical contact areas 30 and
hence the formation of precisely defined active regions 45, a
dielectric layer, for instance silicon dioxide, can be applied (not
shown) on the entire mains surface 14 apart from the electrical
contact areas 30.
The following FIGS. 3A to 5B show measurements with a laser light
source in accordance with the exemplary embodiment in FIGS. 2A to
2C in comparison with a comparative laser light source, which show
the advantageous method of operation of the surface structure
having first and second depressions as described here.
FIGS. 3A and 3B show power characteristic curves for a comparative
laser light source (FIG. 3A) and a laser light source in accordance
with an exemplary embodiment (FIG. 3B). In this case, the abscissa
shows the current in amperes impressed on the comparative laser
light source and the laser light source. The curves 901 (square
symbols) show in conjunction with the right-hand ordinate the
required voltage in volts, while the curves 902 (rhombic symbols),
in each case in conjunction with the left-hand ordinate indicate
the emitted power in watts.
In this case, the laser light source taken as a basis for the
measurement in FIG. 3B is embodied as described in the previous
exemplary embodiment and has a total width of 1 cm. The second
partial regions have an aperture angle of 4.degree.. The first
partial regions have a width of 4 .mu.m, which increases in the
second partial regions to a width of 100 .mu.m at the radiation
coupling-out area 12. The radiation coupling-out area 12 is coated
with a reflection-reducing layer having a reflectivity of 1%. The
emitted electromagnetic radiation has a wavelength of 940 nm. The
first depressions 6 have no absorbent material.
In contrast thereto, the comparative laser light source has no
first depression 6 and hence no optical decoupling of the active
regions 45. The second partial regions of the comparative laser
light source have an aperture angle of 3.degree..
With regard to the emitted power, for the comparative laser light
source, a saturation behavior and also steps brought about by
feedback effects and optical crosstalk can clearly be discerned in
the power characteristic curve 902. The maximum emitted power
reaches approximately 34 W given a current of 70 A. In contrast
thereto, the power characteristic curve 902 of the laser light
source in accordance with the exemplary embodiment described here
has a linear profile and a power of approximately 58 W given a
current of 70 A.
FIGS. 4A and 48 show beam caustic curves for a comparative laser
light source (FIG. 4A) and a laser light source in accordance with
an exemplary embodiment (FIG. 4B). Here the abscissas show in each
case the distance from the radiation coupling-out area 12 in the
emission direction 90 in millimeters, while the ordinates show in
each case a distance from the beam center in micrometers. Here the
curves 903 show lines equal to intensity in a beam center plane
parallel to the extension plane of the semiconductor layer sequence
10 ("x-direction"), while the curves 904 show lines equal to
intensity in a beam center plane perpendicularly thereto
("y-direction"). In this case, the measurements were carried out by
means of a Spiricon beam propagation analyzer.
In contrast to the measurement in FIGS. 3A and 3B, the comparative
laser light source in this measurement has neither first nor second
depressions.
In particular, the curves 903 and 904 show the lateral position
with respect to the beam center point in x- and y-directions at
which a predefined intensity is attained. The beam quality factor
M.sup.2 known to the person skilled in the art can be determined
from the gradient of the curves and also the respective minimum,
which indicates the distance between the beam waist and the beam
center point. For the comparative laser light source, M.sup.2 in
the x-direction is approximately 7, while M.sup.2 for the laser
light source in accordance with the exemplary embodiment in the
x-direction is approximately 2.2.
FIGS. 5A and 5B show coupling-in efficiencies for a comparative
laser light source (FIG. 5A) and a laser light source in accordance
with an exemplary embodiment (FIG. 5B). In the case of this
measurement, the comparative laser light source once again has no
first and second depressions. The abscissas show in each case the
impressed current in amperes. The points 905 (open squares) show
the coupling-in efficient (in %) of the electromagnetic radiation
emitted by the comparative laser light source and laser light
source into an optical fiber having a diameter of 600 .mu.m and a
numerical aperture (NA) of 0.2. The points 906 (filled squares)
show the coupling-in efficiency (in %) of the electromagnetic
radiation emitted by the comparative laser light source and laser
light source into an optical fiber having a diameter of 400 .mu.m
and an NA of 0.2.
While the measurement in FIG. 5A for the comparative laser light
source without first and second depressions given a current of 70 A
reveals a coupling-in efficiency of approximately 79% for the 600
.mu.m fiber and a coupling-in efficiency of approximately 66% for
the 400 .mu.m fiber, corresponding coupling-in efficiencies of 89%
for the 600 .mu.m fiber and 86% for the 400 .mu.m fiber can be
achieved with the laser light source in accordance with the
exemplary embodiment. Losses at the lens surfaces of the
coupling-in optical units are respectively taken into account
here.
Furthermore, measurements were carried out in which comparative
laser light sources having different aperture angles in the second
partial regions were used. On average, with these comparative laser
light sources, given a current of 70 A, a coupling-in efficiency of
approximately 75% into a 400 .mu.m fiber is achieved, which should
be compared with the coupling-in efficiency 906 of 86% shown in
FIG. 5B.
The measurements shown and described here clearly reveal that a
high emission power with at the same time high beam quality can be
made possible precisely by the combination of the first and second
depressions.
Furthermore, a stacking of second or a plurality of the laser light
sources shown is possible in order to achieve an increase in the
emitted power. In this case, powers of approximately 1000 W per
stack are possible in the case of coherent coupling, and powers of
approximately 3000 W in the case of incoherent coupling.
The invention is not restricted to the exemplary embodiments by the
description on the basis of said exemplary embodiments. Rather, the
invention encompasses any novel feature and also any combination of
features, which in particular includes any combination of features
in the patent claims, even if this feature or this combination
itself is not explicitly specified in the patent claims or
exemplary embodiments.
* * * * *